struct.c: fix warning message

* struct.c (new_struct): fix warning message, class name and encoding.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43440 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-10-28

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43441 b2dd03c8-39d4-4d8f-98ff-823fe69b080e